A cryptosystem is an encryption and decryption algorithm for a message. If Alice wants to send a message \(p\)  to Bob, the encryption algorithm \(E\)  computes the cyphertext \(z\)  starting from a key \(K_A\) , i.e. \(z=E(p,K_A)\) . Bob uses the decryption algorithm \(D\)  to recover \(p\)  from a key \(K_B\) , i.e. \(p=D(z,K_B)\) . Of necessity, for all \(p,K_A,K_B\) , \(D(E(p,K_A),K_B)=p\) . Cryptosystems are called private key, if the parties know each other and have shared informations about their private keys, or public key if it is not necessary that the two parties know each other, and they have two public keys. The best known private key algorithms are \(DES\)  (Data Encryption System) and its successor \(AES\)  (Advanced Encryption System). The reader can find more information on cryptography in [1]}. One of the most importand features for cryptographic algorithms is the confusion, i.e. the relation between any bit and all the plaintext appearing random. After the linear cryptanalysis techniques of A. Matsui [2]}, one of the research item in cryptograph was to find functions as far as possible from the linear functions, i.e. maximizing the Hamming distance, in order to resist to linear attacks, see [3]}. Among the family of Boolean functions, such functions are called bent functions. In [4]}, [5]} it is given a characterization of bent functions in terms of strongly regular graphs. Here, we give considerations on parameters of such strongly regular graphs, and a firs characterization of \((n,m)\) -bent functions.
